The present invention relates to a method and a system for precise discharge determination, and more particularly to a method and a system for precise discharge determination for discharging a material such as resin at a constant discharge amount by utilizing an air pressure applied to the inside of a container containing the material to be discharged.
In the processes for fabricating a semiconductor device, a semiconductor chip is bonded to a lead frame. Prior to bonding the semiconductor chip onto the lead frame, it is necessary to have previously supplied a predetermined amount of adhesive onto the lead frame. The semiconductor chip is placed on the adhesive which has already been applied on the lead frame before the semiconductor chip is press-bonded to the lead frame. If the amount of the adhesive applied on the lead frame is insufficient, this results in an insufficient adhesive strength. If, however, the amount of the adhesive applied on the lead frame is excessive, the adhesive is spread to the periphery of the semiconductor chip. To avoid those problems, it is required to precisely control the amount of the adhesive to be applied onto the lead frame. For this purpose, there was proposed a discharge determination system for discharging a predetermined amount of the adhesive. The typical discharge determination discharge system is an air-pressure discharge determination system wherein pressured air is supplied into a container having contained the adhesive to cause the adhesive discharged via a discharge nozzle. This air-pressure discharge determination system is so designed as to enable easy control of the amount of the adhesive discharged by controlling the air pressure and the discharge time.
If a volume of the container containing the adhesive is not so high as compared to the amount of the adhesive discharged one time, this results in that the volume of air in the container is increased by discharge of the adhesive whereby the discharge pressure in the container is gradually reduced even though the air pressure applied into the container and the discharge time remain unchanged. As a result, the amount of the adhesive discharged becomes somewhat small.
In order to settle the above problems with a slight reduction in the amount of the adhesive, it was proposed that waveforms of the air pressure applied into the container containing the adhesive are detected for finding a difference between an integral value of the detected pressure waveforms and an integral value of the predetermined reference pressure waveforms so that the discharge condition is adjusted to compensate that difference. This technique is disclosed in the Japanese patent application No. 5-67057.
In the above discharge system, it is required to preliminarily obtain the reference pressure waveform by discharging as a test all of the adhesive from the container under the same condition as those intended to be selected. For this reason, such preliminary discharging test for obtaining the reference pressure waveform has to be carried out every time when the kinds and amount of the adhesive to be practically used are different. This complicated processes would be inconvenient for the user. Particularly if the volume of the container for containing the adhesive is large, then a long time is taken to completely discharge all of the adhesive stored in the container and such operation would be inefficient.
If accidentally any part of the air pressure system becomes inoperable, the pressure waveform of the actual discharge of the adhesive may largely differ from the reference pressure waveform. In this case, however, such accident might not be detected and thus the normal control of the discharge condition could never be made, for which reason it is no longer possible to make a proper control of the amount of the adhesive discharged, resulting in a large number of inferior products being produced.
Further if variation over time in electrical properties such as drift appears on the electric device such as amplifier or analog-to-digital converter provided in the discharge system, such variation might not be detected and thus the normal control of the discharge condition could never be made, for which reason it is no longer possible to make a proper control of the amount of the adhesive discharged, resulting in a large number of inferior products being produced.
In the above circumstances, it had not been required to develop novel method and system for precise determination discharge of the adhesive, which are capable of keeping the precise determination discharge by automatic compensation to any change of the discharge conditions such as the kind and amount of the adhesive and to variations of the discharge amount caused by any accident having appeared on the apparatus or by variation over time in electrical properties such as drift appears on the electric device such as amplifier or analog-to-digital converter provided in the discharge system.